"O you who believe, Fasting has been enjoined upon you as it was enjoined upon those before you, so that you may be God-fearing." [Al-Baqarah: 183].

Regarding the voluntary fasts, the Prophet - may peace and blessing be upon him – have made the whole year a legitimate period for observing voluntary fast except the ones prohibited by the texts or specified for fasts. But He - may peace and blessing be upon him – encouraged to fast some specific days; as the day of Arafah for non-pilgrims, the day of Ashura, and three days of each month which are: "white days", the Mondays, the tenth of Zul Hijjah (month of Hajj), and so on. It was narrated by Muslim via Abu Qatada Al-Ansaari - may Allah be pleased with him – that the Prophet - may peace and blessing be upon him – was asked about fasting a day and breaking the other day, and he said: "That is the fast of my brother Daa'ud – peace be upon him", he said, and he was also asked about the fast of Monday, he said: "That's the day I was born, and the day I was sent to humanity as prophet or the day of Revelation". He said: and the prophet said: "Fasting three days of every month and from Ramadan to Ramadan equal to the whole lifetime fasting", and he was asked about fasting the day of Arafah, and he said: "that expiates previous year and the next year". He said: He was asked about fasting on the day of Ashura and he said "that expiates the previous year". [Sahih Muslim 3/812 book of fasting].

At the same time the Prophet forbade the exaggeration and excessiveness in worship in general and fasting in particular, because Islam calls for moderation in everything. So it did not authorize the fast of the whole lifetime. In contrast it is prohibited by the saying of the prophet: " He who fasts all the year is as he who did not fast at all. The fasting of three days (a month) will be equal to the fasting of the whole year." [Sahih Al-Bukhaari, Book of Fasting: The fasting of Daa'ud, 1979].

Then it was narrated by Bukhari that Abdullah ibn Amr ibn al-Aas reported that the Prophet told him: " Does three days' fasting in a month not suffice you? I said: Messenger of Allah, (I am capable of observing more). He said: (Would) five (not suffice for you)? I said: Messenger of Allah, (I am capable of observing more) He said: (Would) seven (fasts) not suffice you? I said: Messenger of Allah, (I am capable of observing more). He (the Prophet) then said: (Would) nine (fasts not suffice you)? I said: Messenger of Allah, (I am capable of observing more). He said: (Would) eleven (fasts not suffice you)? I said: Messenger of Allah, (I am capable of observing more than these). Thereupon the Messenger of Allah - may peace and blessing be upon him – said: There is no fasting (better than) the fasting of David which comprises half of the age, fasting a day and not fasting a day." [Previous reference, 1980].

Voluntary fasting is not linked to a certain time, but the Prophet – may peace and blessing be upon him - forbade fasting some specific days, like the two Eids, the three days of Tashreeq, the day of doubt, choosing Friday for fasting unless you fast the day before it or the day after. It was Narrated by Muslim from Abu Huraira - may Allah be pleased with him - that the Messenger of Allah - may Allah bless him and grant him peace - forbade fasting on two days - the day of the Eid al-Fitr and the day of the Eid al-Adha. [Sahih Muslim 2/799 Book of fasting, the prohibition of fasting days of Eid al-Fitr and Eid al-Adha 1138].

It was narrated by Al-Bukhari from Muhammad ibn Abbad, he said: "I asked Jabir "Did the Prophet – may peace and blessing be upon him - forbid fasting on Fridays?" He replied, "Yes." [Sahih Al-Bukhari, Book of Fasting, fasting Fridays, 1984] as he also narrated via Juwairiyyah bint Al-Haarith that the Prophet – may peace and blessing be upon him - entered upon her on Friday while she was fasting. He asked: Did you fast yesterday ? She said: No. He again asked: Do you intend to fast tomorrow ? She said: No. He said: So break your fast" [Sahih Al-Bukhari, 1987]

Muslim narrated via Nubaisha al-Hudhali that Allah's Messenger – may peace and blessing be upon him - said: "The days of Tashriq are the days of eating and drinking." [Sahih Muslim, 2/800 – Book of Fasting, prohibition of fasting the days of Tasriq 1141].

Al-Bayhaqi narrated via Abu Huraira that the prophet – may peace and blessing be upon him – prohibited the fasting of a day before Ramadan, Eid Al-Adha, Al-Fitr, the Tashriq Days and three days after the day of Nahr" [Assunan Al-Kubra Lil-Baihaqi (4/208), Book of Fasting, prohibition of welcoming the month of Ramadan by fasting a day or two days and the prohibition of fasting the day of doubt (7742)].

The summary of all this is that: Fasting is permissible every day of the year except the days in which fasting has been prohibited or the prohibition of the fact of specifying it for fasting without evidence.